The conventional construction of support plates includes a deformed steel plate with an extrusion surrounding a circular opening, a flared steel tube, and a height adjustment lever. Usually, a formed piece of steel wire with a pivot point and a plastic handle serves as the height adjustment lever. The metal plate is typically blanked and formed in a series of individual dies, or alternatively it may be processed through one die with multiple stations incorporating all of the operations necessary to achieve the desired specification and performance of the part.
The steel tube is precut to a specific length, and deburred. It is then flared, and the inside dimension of the tube is sized to accept a centre post or cylinder assembly. The sizing operation is usually done in a forming die. To produce a seat plate assembly, the flared steel tube is located through the extrusion in the metal plate, and welded in place. The adjustment lever is pushed through a pierced opening in the side of the plate, and the end of the wire is centred over the flared tube. The lances in the plate are then formed over the pivot pin to secure the lever to the plate and ensure proper operation.
Alternative prior art seatplate assemblies incorporate a plate along with varying numbers of brackets, a tube and a lever as part of the seat mechanism. Such assemblies are prone to fracturing at the location of the weld bead around the flanged tube where it meets the plate. The safety of such prior devices is currently under review as a result of several accidents and subsequent lawsuits.